Sounds good. I will just buckle down and stay the course. As I encounter these
servers, I have been attempting to reach out to all of the organizations whose
DNS servers exhibit this behavior. Some are less responsive than others, as in
completely ignored. :/
Thanks for the feedback.
________________________________
From: Mark Andrews <ma...@isc.org>
Sent: Friday, January 6, 2023 2:57 PM
To: Justin Krejci
Cc: bind-users@lists.isc.org
Subject: Re: DNS Cookies Causing FORMERR
Really there are very few servers that are broken and the numbers are
decreasing. They are well under 1%. Just contact the few remaining server
operators and inform them that they are broken. It should just be an upgrade
to the current version to fix.
The behavior for unknown EDNS options was tightened nearly 10 years ago (April
2013). It was unspecified in the original EDNS RFC and made ignored in in the
updated RFC which every vendor should have picked up. At the time some vendors
ignored unknown options and others returned FORMERR or NOTIMP or REFUSED.
Others just dropped the request. Some returned BADVER. It was a mess.
There are also implementations that don’t know how to return FORMERR properly.
You don’t echo back the request with rcode set to FORMERR and QR to 1 as that
produces broken responses but some implementations do that. Why would you send
a message that you don’t understand? Nowhere is there any instructions to do
this.
To send a FORMER you send a DNS message header with rcode set to FORMERR. If
you can parse the question section for QUERY copy that into the response. If
you understand EDNS you can add an OPT record. Similarly TSIG if appropriate
and you support it Yes you can sign a FORMERR.
--
Mark Andrews
On 7 Jan 2023, at 06:50, Justin Krejci <jkre...@usinternet.com> wrote:
DNS Servers that do not properly support or properly ignore DNS cookies and
instead return FORMERR is annoying. This is not new. However I have been seeing
more or perhaps just have more users that are finding more domains that are
hosted on authoritative servers with this unfortunate behavior.
Example progrowth.com name severs.
Individual work arounds on caching BIND servers are not difficult to implement,
like this
server 47.206.74.18 {
send-cookie no;
};
server 209.131.228.178 {
send-cookie no;
};
However this workaround is problematic in terms of ongoing upkeep of this list
and the increasing need to add new entries to the list. I'd like to be able to
start sending cookies again if the servers begin to operate compliant to the
EDNS RFC and I would like to not have to write any tools to remove entries from
this list or schedule some regular calendar reminder to check or add to Nagios
or whatever. I'd also rather not just globally disable sending of DNS cookies
but it is something being considered.
In this article @ https://kb.isc.org/docs/aa-01387 it states near the bottom
"Nevertheless, mishandling of the COOKIE option has been known to cause errors
that are fatal to name resolution when the resolver is validating responses
coming from a signed zone, and the authoritative server returns either FORMERR
or BADVERS, or fails to respond to the query. named treats these answers as if
the server does not support EDNS (which it doesn't) so it stops sending any
EDNS queries at all, which makes it impossible to get a DNSSEC response back."
This statement indicates this fall-back method is only applicable to signed
domains. Is there a knob in BIND to apply this behavior to all domains?
Basically, if the authoritative server is behaving incorrectly in this way then
enable no-EDNS or no-COOKIE mode in the interest of allowing DNS queries to
continue to be answered for the end users.
My caching servers are running the BIND 9.18 branch
Thanks for any pointers or suggestions.
-Justin
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